#include 

int findInArray(
       double value,
       int N,
       double a[N]
) {
    for (int i = 0; i < N; ++i) {
        if (a[i] == value) {
            return i;
        }
    }
    return -1;
}

int main() {
    double X[] = {1.2, 3.4, 5.6, 7.8};
    double someValue = 3.4;
    
    int index = findInArray(someValue, 4, X);
    
    printf("Found at position %d, value %lf\n", index, someValue);

    return 0;
}